The world of American football is abuzz after Brandon Marshall, a Chicago
Bears player suggested that some players were using Viagra hoping it would
give them an advantage during games.

Marshall started the speculation, and jokes, on Wednesday when asked about a growing number of suspensions tied to amphetamines, including the ADHD drug Adderall. He said he did not know much about Adderall, but suggested Viagra could be viewed by players as a way to boost their energy.

"I know guys, it's such a competitive league, and guys try anything just to get that edge," he said. "I've heard of guys using Viagra, seriously, because the blood, it's supposed to thin ... I don't know. Some crazy stuff. It's kind of scary with some of these chemicals that are in some of these things, so you have to be careful."

NFL spokesman Greg Aiello said Viagra is not a banned substance and declined further comment.

Bears defensive back D.J. Moore wondered if Marshall was kidding and said: "I've never heard of that."

"I didn't even know people could do that," New York Giants tight end Martellus Bennett said. And his team-mate Justin Tuck added: "I can't imagine why people would take steroids, so I have no comment on Viagra. Besides, my wife would be very upset with me."

Dr Olivier Rabin, science director at the World Anti-Doping Agency in Montreal, said it is unlikely Viagra does anything to improve football performance in NFL players. He also said there is no evidence the drug might somehow mask the use of steroids or other performance-enhancing drugs.

Dr Rabin noted that research in high altitudes found the drug helped improve oxygen flow in climbers with impaired lung function. Viagra can dilate blood vessels, and vessels in the lung constrict in high altitudes.

Research involving cyclists at high altitudes found similar benefits, but Dr Rabin said studies have shown the drug has no effect on athletic performance at sea level.

University of Miami researcher Kevin Jacobs has studied Viagra in simulated high-altitude environments and "didn't find much benefit in young, healthy, active individuals."

"No one has really tested it in football players doing exercise. Whatever benefit they think they're getting is probably more psychological than anything," said Jacobs, an associate professor in the kinesiology and sport sciences department.